Ultrafast dynamics of transient bleaching of surface modified cadmium sulphide nano-particles in Nafion films

Ultrafast dynamics of transient photobleaching and recovery of cadmium sulp hide (CdS) nanoparticles in Nafion films before and after treatment with ex cess cadmium ions have been studied upon excitation at 400 nm with a femtos econd laser system. Both samples gave transient bleaching in less than 1 ps and a multi-exponential recovery in the wavelength region between ca. 410 and 500 nm. Cd2+ treatment of the nanoparticles resulted in several dramati c changes to the fluorescence and transient bleaching spectra from the film s: (1) A new fluorescence band at higher energy appeared in addition to an increase in the 'defect' fluorescence band at longer wavelengths. (2) A rem arkable increase in the extent of transient bleaching was observed below ab out 440 nm, which recovered faster than that at longer wavelengths. (3) The recovery rate of the transient bleaching became faster, relative to the un treated nanoparticles, over the whole wavelength region of the bleaching. T hese results have been interpreted in terms of the recombination of photoge nerated electrons and holes from traps or defects in/on the nanoparticles. (C) 1999 Elsevier Science B.V. All rights reserved.